Prior generations of many motion picture photographic film elements that are used as print films for movie theater projection have long used a carbon black-containing layer on the backside of the film. This backside layer provides both antihalation protection and antistatic properties prior to film processing, as well as reasonable friction (necessary for both roller conveyance and also in the film roll handling/winding process) even when the emulsion coating protective layer had elevated levels of lubricant (for scratch/abrasion protection). The carbon black is applied in an alkali-soluble binder that allows the layer to be removed by a process that involves soaking the film in alkali solution, scrubbing the backside layer, and rinsing with water, leaving bare support on the non-emulsion side of the film. The bare support has excellent wear and scratch properties, and the emulsion side can be protected by the elevated levels of lubricant surviving the processing. This carbon black removal process, however, which takes place prior to image development, is both tedious and environmentally undesirable since large quantities of water are utilized in this film processing step. In addition, in order to facilitate removal during film processing, the carbon black-containing layer is not highly adherent to the photographic film support and may dislodge during various film manufacturing operations such as film slitting and film perforating. Carbon black debris generated during these operations may become lodged on the photographic emulsion and cause image defects during subsequent exposure and film processing.
After removal of the carbon black-containing layer, antistatic properties provided thereby are lost. Undesired static charge build-up can then occur on processed motion picture print film when transported through projectors or on rewind equipment. While discharge of high static charges does not cause static marks on the processed photographic film as the film's light sensitive silver halide has also been removed during film processing, high static charges can attract dirt particles to the film surface. Once on the film surface, these dirt particles can create abrasion or scratches or, if sufficiently large, the dirt particles may be seen on the projected film image.
U.S. Pat. No. 5,679,505 describes a motion picture print film which, in place of a carbon black-containing layer on the backside of the film, contains an antihalation undercoat on the front side of the film support under the film emulsion layers, and an antistatic layer and a protective topcoat on the backside of the support. The backing layer protective topcoat is comprised of a polyurethane binder and lubricant. The polyurethane binder has a tensile elongation to break of at least 50% and a Young's modulus measured at 2% elongation of at least 50000 lb/in2. Despite the toughness of this overcoat, abrasive wear and the subsequent dust generation have continued to be a problem with backing layer protective topcoats in motion picture print film. During the lifetime of a print in a theater, abrasions in the perforation area can become severe enough that the soundtrack is damaged. In addition, dust can build up in the picture area of the film and reduce the quality of the projected image.
One approach that greatly reduces projector dust is to heavily lubricate the backside protective overcoat. However, at the lubricant levels necessary to reduce dusting in projectors, the coefficient of friction of the overcoat is reduced to the point that such a film is non-manufacturable because support rolls have insufficient traction for satisfactory conveyance in high speed sensitizing machines, and also because the long, slit rolls of photographic film become telescoped or dished in storage or shipping, wherein the roll integrity is at risk.
U.S. Pat. No. 6,326,131 discloses one solution to the problem of providing both high lubrication as well as desired friction. In such disclosure, an additive is included in the lubricant containing backside protective overcoat layer, where the additive is selected to be immiscible with and more surface active than the lubricant, and is added in an amount effective to increase the coefficient of friction for the overcoat layer. Tetraethylammoniun salt of perfluorooctyl sulfonic acid (Fluorotenside FT-248 by Bayer, A.G.), e.g., is disclosed as a specific example of an effective additive which maybe added to a highly lubricated backside protective overcoat to raise the coefficient of friction of such overcoat. This, along with limiting lubricant levels in the imaging side protective overcoat layer, can result in adequate conveyance and winding performance. There have recently been efforts to minimize the use of perfluorooctyl sulfonate (PFOS) based surfactants, however, and accordingly it would be desirable to find alternatives to use of such material as a friction improving additive in highly lubricated layers.
The incorporation of matting agents in the outermost layers of photographic elements is well known. These matting agents can reduce the potential for a photographic film to ferrotype when the backside of the film is in contact with the front side (i.e., emulsion side) of the film under the pressures that are typical of, for example, a tightly wound roll of film. Ferrotyping may cause the two sides of the film to stick together, and, under severe cases of ferrotyping, damage to the emulsion side surface layer may occur when the roll is unwound. In some cases, ferrotyping may have an adverse effect on the sensitometric response of the photographic emulsion. Matting agents are also employed for such purposes as reduction of static charging and excessive sheen, pencil mark acceptance and avoidance of Newton's rings. A wide variety of materials have been employed as matting agents including both inorganic and polymeric fine particles as illustrated by Research Disclosure, Item 38957, pages 615-616, September 1996.
Large quantities of matting agents are often employed for the purposes described above. However, the use of a large quantity of matting agent may result in undesirable side effects such as increased haze and graininess of the processed image. To overcome these limitations, a matting agent that is removed during film processing is often employed in place of “permanent” matting agents. Such “removable” or “soluble” matting agents are typically alkali soluble polymeric matte particles comprising, for example, a copolymer of methyl methacrylate and methacrylic acid. Soluble matte particles are described, for example, in U.S. Pat. Nos. 2,322,037; 2,992,101; 3,767,448; 4,094,848; 4,142,894; 4,447,525 and 4,524,131. Because these matte particles are removed during film processing, they can generally be employed in the photographic film at relatively high dried coating weights, for example, 200 mg/m2 or more of matte particles, without excessively impacting haze. However, in some cases the use of large quantities of even soluble matting agent may result in undesirable side effects. Soluble matte beads have a tendency to swell or dissolve during preparation, delivery, or coating of the solution containing the matte beads thus causing various types of coating defects in the film. During film processing, the removal of soluble matte beads may leave behind pits or craters in the coating, these may be visible especially under the very high magnifications typically used for viewing a motion picture print film, for example. Further, the use of large quantities of soluble matting agent (as well as permanent matting agent) may generate a fine dust of particles due to the matting agent being dislodged from the unexposed and unprocessed film during film manufacture and use. As with carbon black and other dirt particle debris, the matte dust generated may become lodged on the photographic emulsion and cause image defects during subsequent exposure and film processing. In addition, these dislodged particles may scratch and abrade the photographic film.
Any matting agent (permanent or soluble) used in motion picture print films can also potentially affect image quality and soundtrack reproduction during theater viewing. Large amounts of permanent or soluble matting agent present in a print film emulsion overcoat during printing of the print film from a duplicate negative will result in image graininess during projection. Even moderate amounts of permanent matting agent present on either side of the exposed and processed print film can affect image graininess during projection. Soundtrack reproduction quality (i.e., frequency response and signal-to-noise ratio) may be degraded at substantially lower matting agent levels than those necessary to affect image quality, this is especially true for those films that utilize a digital soundtrack. U.S. Pat. No. 5,679,505 referenced above, e.g., describes photographic element especially useful as a motion picture print film comprised of a support having on one side an antihalation undercoat and at least one silver halide emulsion layer and having on the opposite side an antistatic layer and a protective backing layer topcoat comprised of a polyurethane binder. The backing layer topcoat includes from 1 to 100 mg/m2, preferably from 15 to 65 mg/m2, of matte beads. Examples in the '505 patent teach a backing layer topcoat having 30.7 mg/m2 permanent matte and an emulsion overcoat having 5 mg/m2 permanent matte.
Relatively low Tg crosslinked elastomeric matting agent particles have also been disclosed for use in photographic elements. U.S. Pat. No. 5,786,298, e.g., discloses the use of crosslinked elastomeric matte beads having a Tg of 10° C. or less in a backing layer to reduce scratches and abrasions which may be formed in the imaging side of the element. U.S. Pat. No. 5,800,973 discloses the use of crosslinked elastomeric matte beads in combination with hard filler particles in an imaging element backing layer. U.S. Pat. No. 5,916,741 discloses the use of crosslinked elastomeric matte particles in photographic element layers to reduce pressure sensitivity and dusting characteristics in transport and finishing operations. The prior art has not suggested, however, the use of a relatively lower amount of low Tg crosslinked elastomeric matte particles in combination with conventional high Tg matte in a highly lubricated photographic element.
It would be desirable to provide photographic film elements with highly lubricated protective layers on both the backside and the image layer side in order to provide increased wear protection in addition to adequate conveyance and winding performance.